One state-of-the-art aerating device is known (cf. an advertising prospectus "Brandol area" of Messrs Schumacher GmbH & Co.KG, Germany, 1989) to comprise a tubular air conduit provided with radial holes arranged lengthwise one of the generatrices thereof. A cylinder-shaped dispersing member is held to the peripheral surface of said tubular air conduit above each of said holes, said element being plugged at both ends.
The aforesaid aerating device features a high degree of dispersion of the compressed air fed into the liquid being aerated. However, a sophisticated construction of their attachment to the air distributor affects adversely the operating reliability of the aerating device, because compressed air may make its way into the liquid at the place of attachment of the dispersing member to the air distributor.
Another state-of-the-art aerating device is known (cf. the textbook "Aerators for sewage water treatment" by B. M. Khudenko et al., Stroiizdat Publishers, Moscow, 1973, p.36 (in Russian) to comprise a header for feeding compressed air to the aerating device, said header communicating with an air conduit assembled from a plurality of series arranged aerating modules tightly held together, each of said modules having a tubular member provided with at least one radial hole, and a disperser located outside of said tubular member and communicating therewith by compressed air through said radial hole.
The aforesaid known aerating device makes use of dome- or disk-type disperser disposed horizontally above the tubular member. The dispersing member of the disperser together with the baseplate defines an air-tight space to which compressed is admitted to pass from the tubular member. The disperser is joined together with the tubular member by a fastening bolt through which compressed air is fed. The disperser-to-tubular member attachment point is made air-tight due to the provision of a rubber gasket.
A water-air flow is established above the disperser during operation of the known aerating device, said flow moving at a velocity of 1 to 3 m/s so as to saturate the liquid under aeration with air bubbles. In this case larger air bubbles appear above the central disperser portion in the area where compressed air is fed thereto, which affects adversely mass-exchange processes occurring in the liquid being aerated.
Furthermore, an ascending water-air flow develops a rarefaction zone in the surrounding liquid, with the result that the sludge settled on the aerotank bottom gets involved in the flow motion. However, a considerable proportion of the sludge is stuck to the disperser bottom portion and to its side and a top portion adjacent to the bottom portion thereof. This reduces an active disperser surface and decreases the degree of aeration of sludgy sediments which in turn affects the vital activity of microorganisms living in said sediments. A higher air flow rate fails to eliminate sludge sticking to the disperser.
The width of the aeration belt can be changed in the known aerator depending on specific operating conditions by using dispersers of another diameter, which involves complete dismantling of the whole system and is therefore technically hard to perform. Use of larger-diameter dispersers and an increased air flow rate might result in the course of operation in inadmissible vibration which is liable to destroy the disperser-to-air conduit attachment points.
The fact that the dispersing member is joined together with the baseplate and both of them are held to the air conduit by a bolt through which compressed sir is fed results in loss of air-tightness in the course of aerator operation, which affects the mass-exchange processes.